One type of a conventional optical isolator comprises a polarizer, a 45 degree - Faraday rotator, and an analyzer which are fixed by applying optic adhesive between the polarizer and the Faraday rotator and between the Faraday rotator and the analyzer, and a magnet which is fixed to an outer periphery of the Faraday rotator by use of adhesive.
In operation, incident light is supplied to the polarizer of the optical isolator, so that a polarization component of the incident light coinciding with a polarization plane of the polarizer is passed through the polarizer to be supplied to the Faraday rotator, from which a light having a polarization rotated by 45 degrees is supplied. The light having the polarization rotated by 45 degrees is passed through the analyzer, so that output light is supplied from the analyzer of the optical isolator. On the contrary, return light propagating in the direction opposite to that of the incident light is stopped by the polarizer, after it is passed through the analyzer and the Faraday rotator. The detailed structure and operation will be explained later.
According to the conventional optical isolator, however, there is a disadvantage in that anti-humidity property is not so high, because the polarizer, the Faraday rotator and the analyzer are fixed on optical planes by the optic adhesive. Thus the conventional optical isolator does not operate satisfactorily under high temperature and high humidity.